97 4.0 runs bad at 1500-1900 rpm

My 97 Ranger runs rough, vibrates at rpm of 1500-1900. Engaging the brake at a stop sign smothes it out but it chugs at low speed before I stop. When getting up to speed, it runs awsome above 2000 rpm while accelerating, but as the auto tranny shifts and the rpm drops below 1900 it runs rough. The CEL came on, and according to Auto Zone code reader it was PO74, the O2 sensor behind the cat. It has 134,000 miles, gets bad milage, under 12 mpg. If the engine was worn out, would it just be having a problem at 1500-1900 rpm? Could this be a symptom of the O2 sensor?

thanks

I think that you answered you own question. The OBD code says that the fault lays in the O2 sensor. Maybe you should change the O2 sensor? 133 K seems about right...:sarcasm1: and no, it is not likely a worn out engine, at 133K. Probably a worn out O2 sensor. About $60 give or take..

Yes, but is this problem the symptom of an O2 sensor going bad?

Yes thats the signs of the O2 sensor post cat. Easy to replace. Parts gonna be about 55 bucks. I recomend soaking it well in WD40 after it cools down and letting that soak in over night. I ended up having to put a pipe wrench on mine to break it free, but it was easy after that. Might not be bad idea to cange out the others also. This may help your fuel milage out a bit.

Hope that helps.

JP

I took it to the Stealer, and after spending $307.00 on their diagnosis machine, it turned out to be the spark plug wires, and #2 and #5 plug were oily. It now runs better than it ever has. I think it burns oil, fouling the plugs. The plugs were replaced 3000 miles ago and shouldn't get bad that quick. I now know to change #2 and #5 frequently.

Ahh the terrors of OBD 2 read outs. My 98 Ranger threw the code for bad O2 sensor. But the PROBLEM was a bad misfire in # 1 caused by an ignition fault. The raw fuel dumping through the exhaust toasted the O2 sensor. So while the codes tell you what has happened --- they often don't tell you WHY.

I'm still learning. Learning is expensive. The thing is though, I can spend a few hundred learning or give my wallet to the dealer. I think sooner or later I'll come ahead learning. These forums are great since sharing advice causes learning at a much lower cost.